Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$30.73	7.694%	$33.0944	$33.09	$33.10	$33.10
Purchase #2	$38.54	11.459%	$42.9563	$42.96	$42.95	$43.00
Purchase #3	$31.83	8.329%	$34.4811	$34.48	$34.50	$34.50
Purchase #4	$202.52	9.671%	$222.1057	$222.11	$222.10	$222.10
Purchase #5	$157.94	11.226%	$175.6703	$175.67	$175.65	$175.70
Purchase #6	$34.80	5.236%	$36.6221	$36.62	$36.60	$36.60
Purchase #7	$160.78	13.752%	$182.8905	$182.89	$182.90	$182.90
7 purchase totals =	$657.14		$727.8204	$727.82	$727.80	$727.90